Method for minimizing the occurrence of fires during well drilling operations



United States Patent F METHOD FOR MININIIZING THE OCCURRENCE OF FIRESDURING WELL DRILLING OPERA- TIONS John Gordon Jackson, Denver, Colo.,assignor to Well Completions Inc., Denver, Colo., a corporation ofColorado No Drawing. Filed July 13, 1962, Ser. No. 209,755

5 Claims. (Cl. 175-69) This invention relates to a method for minimizingthe occurrence of fire during the drilling of wells, and particularly,during drilling with air and other gases.

Gas drilling of oil wells, that is, drilling with the use of air orother gas as the circulating medium rather than drilling mud, is now anaccepted procedure in-the drilling industry. Ai-r, being a mixture ofgases is referred to herein as a gas, the latter term including a singlegas or a mixture of gases. Among the many advantages of gas drilling isthe fact that bit life is increased by as much as one and one-half timesand drilling times are reduced by a factor of 2 to 5 under ordinaryconditions. In accordance with this procedure air or other gas iscirculated through the well during drilling to perform the function ofdrilling mud. Circulation is usually accomplished by forcing the air orother gas under pressure into the well through the drill pipe and bitand when reversing its travel to the well surface between the outside ofthe drill pipe and the bore hole; however, the circulation route can bereversed. A dual passage drill stern can be used, and other methods maybe used to introduce the gas into the well. The main function of thecirculating gas is, of course, to remove drilling and other foreignmaterial from the well.

One of the disadvantages attendant to the use of air drilling is thefact that the hazard of fire in the well during drilling issignificantly increased. The principal reason for this increase when airis used as the drilling gas is that such use results in the introductionof oxygen in amounts sufficient to support combustion when a gas flow isencountered in the well. The oxygen content of air is around 18 percentand it is established that air containing about 12 percent or more ofoxygen will support combustion under atmospheric conditions.

Combustible and explosive gases present in oil wells which ordinarilycause fires or explosions when mixed with the correct proportion ofoxygen and hydrocarbon gases or mixtures thereof. The most commonlyoccurring of these, of course, is methane. In addition, certaincombustible solid materials such as lignite may constitute some of thesurface of the bore hole. While the agency causing ignition of thecombustible material is not definitely established, it is believed thatheat generated by friction between the drill string and the surface ofthe bore hole, andsparks resulting from contact of the drill or othermetal equipment with rocks may be sources of ignition. While the numberof fires occurring in oil wells is relatively small in comparison to thenumber of wells drilled, the damage from a single fire may be extremelylarge. This is true because it may become necessary to fish the bit ifthe drill string is severed or the well may be lost, either of theseoccurrences resulting in a large financial loss in the Way of equipment,time and labor. This emphasizes the importance of the availability of amethod for the prevention of oil well fires.

Accordingly, it is a principal object of this invention to provide amethod for minimizing the occurrence of fires in wells during airdrilling thereof which method is safe, efiective, and economicallyfeasible.

The invention in its broadest aspects comprises mainair.

3,286,778 Patented Nov. 22, 1966 taining by various means the oxygencontent of the gaseous medium, in wells being drilled, below thatnecessary to support combustion under the temperature and pressureconditions existing in the well.

The temperature and pressure existing in bore holes during drilling varyand are often higher than atmospheric temperature and pressure. Thesehigher temperatures and pressures result in a reduced amount of oxygenbeing required to support combustion. Accordingly, the amount of inertmaterial introduced into the gas stream must be sufficient to reduce theoxygen content of the gaseous medium in the bore hole below thatnecessary to support combustion. This amount can be readily calculatedas the variants necessary for the calculation are well known. Inpractice, conditions are adjusted such that an excess of inert materialis used to insure that inert conditions are achieved in the bore hole.

The invention will be illustrated by an application in which compressedair is used as the circulating medium during drilling to replace mud. Itis not limited to this application as it is equally applicable whenother gases or mixtures of gases are used, particularly, if the gasmixture includes oxygen. As is well known, the rate of introduction ofcompressed gas into a well during drilling is measurable andcontrollable. It is thus a simple operation to calculate the amount ofinert material necessary for introduction 'into a measured quantity ofcompressed air to reduce the oxygen content thereof below that necessaryto support combustion and meter this amount into the gas stream beforeit enters the well. The inert material when introduced may be in solid,liquid or gaseous form, and covers a wide range of materials, one

requirement being that it not have a prohibitively deleterious effect onthe drilling equipment.

When a gas is used as the inert material, it is cleaned and dehydratedwhen necessary before introduction into the compressed air stream. Thegas used preferably should have a higher density than air, should benonexplosive, non-combustible, and otherwise inert so that it does notproduce a corrosive effect on the drilling equipment. In practice,sufficient quantities of inert gases are mixed for re-cycling into thewell, consisting of air and inert material, and this mixture re-cycledcontinuously with replenishment as necessary. Re-cycling is practicedbecause of economic considerations. Obviously when the economicsituation warrants it, a single inert gas rather than air, or a mixtureof such gases, may be used where more effective fire prevention isrequired. The invention includes the maintenance of the gaseous mediumin the well in the required state of inertness not only by introductionof an inert material itself but also by the formation of such a materialin. situ. An example of this is the formation of an inert gas in situfrom materials introduced into the well.

A preferred gas, where the economics of the situation will permit itsuse, is carbon dioxide. This gas is heavier than air, is inert, can beinexpensively manufactured, and is easy to handle. The slight amount ofcarbonic acid which might be formed from contact of this gas withmoisture in the well can 'be economically inhibited. Other gases whichmay be used are helium, argon, nitrogen, other inert gases, and mixturesthereof. -Natural gas and exhaust gases have been used effectively inthe process. These latter two gases contain moisture and othercomponents which result in corrosion ofequipment and they must becarefully cleaned, dehydrated and conditioned before use.

It is to be understood that the term gas or gaseous medium as used inthis specification and claims means not only a single gas but mixturesof gases, and includes The term inert material as used herein meansmaterial which is non-combustible and non-explosive and will not supportcombustion. The term circulating medium includes drilling mud, gas,gaseous medium and other materials circulated through the well duringdrilling to remove drillings and other foreign material from the well.When the oxygen content of a gaseous medium is *below that required tosupport combustion" as the expression is used herein, it is meant thatthe oxygen content is below the amount ordinarily accepted as necessaryfor supporting combustion, this amount being about 12 percent for airunder atmospheric conditions. By fire retardant or fire retardantmaterial is meant material which has the property of blanketing outfires and is commonly used for that purpose. Examples of such materialsare disclosed in U. S. Patent No. 2,858,895. The term exhaust gasincludes engine exhaust gases from internal combustion engines.

When solids are used as the inert material they are used in the form offinely divided powder in which the particle size is ordinarily not over50 microns in diameter. A wide variety of solid materials may be used.The solid material may be introduce into the gas stream by means ofconventional solids injection devices such as that disclosed in U. S.Patent No. 2,907,480. The amount of solids to be introduced is readilycalculable and can be metered into the gas stream by conventionalmetering techniques or machines such as that referred to above. Theextremely small particle size and the introduction of the particles intoa high velocity gas stream results in a suspension of the finely dividedparticles in the air stream. Solid materials which have beensuccessfully used are materials such as dibasic ammonium phosphate,powdered soda ash, borax and various other borates, particularly,calcium containing borates. Other materials which may be used are alkaliand alkaline earth metal carbonates and other ammonium compounds, suchas, ammonium chloride and ammonium sulphate.

Soda ash or a mixture of borax and soda ash, and sodium calcium borateused alone, have been used to good effect as the solid materials tominimize the occurrence of fires during well drilling operations. Inthese applications the solid materials having a particle size of about50 microns were introduced into the gas stream at the rate of about toabout 35 pounds per hour. The volume of the air stream varied from about1500 standard cubic feet per minute to about 5000 cubic feet per minuteat pressures varying from 250 p.s.i.g. to 750 p.s.i.g. This amounts to aratio of about .000017 to .00039 pound of inert material per standardcubic feet of air, The pressure will, of course, not affect the amountof inert material per volume of air which is added but only the rate ofaddition. In applications of the invention like the above solids areintroduced into a fixed volume of air until the correct mixture isobtained and the mixture continuously recirculated in a closed systemwhich includes the bore hole with replenishment of solid material asnecessary. The closed system includes conventional apparatus at thesurface for removal of borings and conditioning by removal of unwantedmoisture and other undesirable materials.

The preferred solid material to be suspended in the gas stream is a fireretardant material such as soda ash, sodium calcium borate, ammoniumphosphate and other equivalent materials, as these materials have a fireretardant effect through coating of the surfaces of the drill pipe andthe bore. The coating of certain combustible substances in the borewall, such as lignite, with fire retardant material results inadditional fire protection. These finely divided materials also have afire retardant effect on the combustible gases present when mixed withthem. Other borates which may be used are calcium borate and mixturesthereof with sodium-calcium borate, and borates occurring in mineralform, such as, colemanite, elexite and mixtures thereof.

The solid material introduced is not restricted to material which itselfreduces the oxygen content of the gaseous medium but includes materialswhich may interact with each other or under the influence of heat toform inert gases, which in turn reduce the oxygen content of the gaseousmedium in the well to the desired amount. For example, carbonates, suchas, sodium bicarbonate and others can be introduced which will decomposeunder the action of heat or interaction with dilute acid to releasecarbon dioxide. For example, a soluble acid salt and bicarbonate of sodaor soda ash can be introduced simultaneously in which case the solubleacid salt will react with slight amounts of water present to form acidwhich will in turn react with the bicarbonate of soda to produce carbondioxide. Frothing agents may also be introduced with the inert material.

Liquids, including suspensions and emulsions, may also be used in therequired amounts as the inert medium. Such liquids are preferablyintroduced in the form of aerosols. For example, they can be introducedin the air stream by piston type injection pumps. A liquid such ascarbon tetrachloride may be used, this liquid being inert andnonreactive with metal drilling equipment so that it does not producecorrosion solutions of inert materials which react under heat to releaseinert gas may be used, Other inert liquid and mixtures thereof may beused. The aerosol formed by introduction of the liquid into the highvelocity gas stream would of course be a suspension of the liquid in theair stream.

The invention is not limited to the introduction of inert materials onlyin the compressed gas stream for oxygen control purposes, but includesintroduction of these materials along with other materials for otherpurposes, such as, frothing agents, wetting agents, agents for moisturecontrol and for other purposes.

It is seen from the above discussion that a method has been provided forminimizing the occurrence of fires in wells which is effective andhighly compatible with gas drilling. The method, in which both gas andsolid materials'have been used as the inert materials, has beeneffectively used with gas drilling and has significantly reduced theincidence of down-hole fires in oil and gas wells in which it has beenused.

The invention is not limited to the particular inert materials andproportions disclosed herein, as these are given for the purpose ofillustration only and other equivalent materials and varyingproportion-s may be used.

It is therefore to be understood that various modifications and changesmay be made in the construction and arrangement of parts of the presentinvention Without departing from the spirit and scope thereof as definedby the appended claims.

What is claimed is:

1. The method of minimizing the occurrence of fire during drilling ofwells wherein air is used as the circulating fluid, which methodcomprises: Introducing into the circulating air materials which react toform a sutficient amount of an inert gas to reduce the oxygen content ofthe air below that which will support combustion.

2. The method of claim 1 in Which said materials decompose under heat toform the inert gas.

3. The method of claim 2 in which one of said materials is sodiumbicarbonate.

4. The method of claim 1 in which said materials are carbonates ofsodium and a soluble acid salt which reacts with water in the bore holeto form an acid.

5. The method of minimizing the occurrence of fires during well drillingoperations in which air is used as a circulating fluid which comprises;injecting into the air before it enters the well, a finely divided inertsolid material selected from the group consisting of alkali metalcarbonates, alkaline earth metal carbonates, dibasic ammonium phosphate,ammonium chloride, ammonium sulphate, and borates of calcium, in anamount conforming to a ratio of about .000017 to .00039 pound of inertmaterial per standard cubic feet of air.

References Cited by the Examiner UNITED 6 FOREIGN PATENTS 740,28911/1955 Great Britain. 812,146 4/1959 Great Britain.

OTHER REFERENCES Bruno, E. R.: Drilling with Air, In the PetroleumEngineer, January 1956, pp. B21-B24.

Buffington, E. C.: Multi-purpose Nitrogen Provides New Drilling Tool, InDrilling, April 196-2, p. 56.

Smith, F. W.: Effective Air Drilling, In the oil and Gas Journal October1959, vol. 57, No. 44, pp. 83-86.

CHARLES E. OCONNELL, Primary Examiner.

D. H. BROWN, Assistant Examiner.

1. THE METHOD OF MINIMIZING THE OCCURRENCE OF FIRE DURING DRILLING OFWELLS WHEREIN AIR IS USED AS THE CIRCULATING FLUID, WHICH METHODCOMPRISES: INTRODUCING INTO THE CIRCULATING AIR MATERIALS WHICH REACT TOFORM A SUFFICIENT AMOUNT OF AN INERT GAS TO REDUCE THE OXYGEN CONTENT OFTHE AIR BELOW THAT WHICH WILL SUPPORT COMBUSTION.